Applications of endoprotheses to the superior femoral artery (SFA) and to the popliteal artery (PA) has received increased attention because of the prevalence of peripheral arterial disease (PAD) among older patients and because no known endoprosthesis can adequately supports the SFA and the PA without distorting its architecture during patient motion.
PAD is estimated to affect between 3% and 10% of individuals till the age of 70 and may approach 20% of individuals older than 70 years of age. PAD has been associated with an increased risk of coronary artery disease, cerebrovascular disease, and premature death. Moreover, as a consequence of limited exercise performance and walking ability, individuals who have symptoms of intermittent claudication experience a significantly negative impact on quality of life.
Exercise programs have been recommended as the first line of therapy for PAD. Pharmacotherapy with cilostazol provides additional symptom relief, but patients who fail medical therapy and continue to have resting leg pain or non-healing ulcers eventually become candidates for invasive treatment strategy. Unfortunately, surgical revascularization has associated with higher periprocedural morbidity and mortality, making the surgical option less desirable in elderly patients—a significant proportion of patients with PAD.
Because greater than 50% of individuals with lower extremity claudication have atherosclerotic disease confined to the superficial femoral artery (SFA), endovascular techniques have recently emerged to treat this arterial segment.
Stents, grafts and a variety of other endoprostheses are well known and used in endovascular procedures, such as for treating aneurysms, lining or repairing vessel walls, filtering or controlling fluid flow, and expanding or scaffolding occluded or collapsed vessels. Such endoprostheses can be delivered and used in virtually any accessible body lumen of a human or animal and can be deployed by any of a variety of recognized means.
An endoprosthesis is typically delivered by a catheter system to a desired location or deployment site inside a body lumen of a vessel or other tubular organ. To facilitate such delivery, the endoprosthesis must be capable of having a particularly small cross profile and a sufficient degree of longitudinal flexibility during delivery to allow advancement through the anatomy to the deployed site.
Once deployed, the endoprosthesis should be capable of satisfying a variety of performance characteristics. The endoprosthesis should have sufficient rigidity or outer bias to perform its intended function, such as opening a lumen or supporting a vessel wall. Similarly, the endoprosthesis should retain sufficient flexibility along its length in its expanded condition so that it will not kink, straighten or fracture during or after deployment in a curved vessel. The endoprosthesis should also provide a substantially uniform or otherwise controlled scaffolding of the vessel wall and prevent plaque from protruding into the artery.
One type of endoprosthesis is the stent, which is used for the treatment of atherosclerotic stenosis in blood vessels. After a patient undergoes a percutaneous transluminal angioplasty or similar interventional procedure, a stent may be deployed at the treatment site to maintain patency of the vessel. The stent is configured to scaffold or support the treated blood vessel and may be loaded with a beneficial agent, acting as a delivery platform to reduce restenosis or the like.
Numerous endoprosthesis designs and constructions have been developed to address one or more of the performance characteristics summarized above. For example, a variety of stent designs are disclosed in the following patents: U.S. Pat. No. 4,580,568 to Gianturco; U.S. Pat. No. 5,102,417 to Palmaz; U.S. Pat. No. 5,104,404 to Wolff; U.S. Pat. No. 5,133,732 to Wiktor; U.S. Pat. No. 5,292,331 to Boneau; U.S. Pat. No. 5,514,154 to Lau et al.; U.S. Pat. No. 5,569,295 to Lam; U.S. Pat. No. 5,707,386 to Schnepp-Pesch et al.; U.S. Pat. No. 5,733,303 to Israel et al.; U.S. Pat. No. 5,755,771 to Penn et al.; U.S. Pat. No. 5,776,161 to Globerman; U.S. Pat. No. 5,895,406 to Gray et al.; U.S. Pat. No. 6,033,434 to Borghi; U.S. Pat. No. 6,099,561 to Alt; U.S. Pat. No. 6,106,548 to Roubin et al.; U.S. Pat. No. 6,113,627 to Jang; U.S. Pat. No. 6,132,460 to Thompson; U.S. Pat. No. 6,331,189 to Wolinsky; and U.S. Pat. No. 7,128,756 to Lowe et al., the entireties of which are incorporated herein by reference.
During the treatment of some types of SFA and PA disease, relatively long stent lengths are frequently required, at times causing the treating physician to overlap multiple stents. Further complicating the treatment of SFA and PA disease is the possibility of stent fractures and subsequent restenosis. A particular area of vulnerability is the area through the adductor canal as the SFA continues behind the knee; in fact, the area at the adductor canal is a frequent location for SFA disease likely secondary to the bending, compression, elongation and torsion forces on the artery itself due to the muscular structure surrounding this canal, leading to a lengthening and shortening of up to 15% of the stent between straight and bent positions of a limb. After the stent has been implanted, the body vessel is subjected to repeated traumas caused by the negative interaction of a relatively rigid stent and a softer artery.
In the earlier days of endovascular therapy, it was believed that the area to avoid stenting due to the risk of stent crush or stent fracture was near the bony articulation between the femur and the tibia. It is now believed that the area of critical importance is really superior to this point leading up to the adductor canal, which is a frequent location of SFA lesions. If it is necessary to stent this region, the ability of the stent to withstand the forces present in the SFA is of critical importance. Another risk is the incidence of restenosis, against which self-expanding Nitinol stents have shown better one-year patency rates than other types of stents.
Therefore, it would be desirable for the endoprosthesis to provide an elevated degree of scaffolding to a vessel wall while retaining an elevated degree of flexibility within the operating environments of the SFA and PA.